(1) Field of the Invention
This invention relates to a process for preparing halogenated benzene derivatives by adsorptive separation.
(2) Description of the Prior Art
Halogenated benzene derivatives typically include dichlorobenzene, chlorotoluene, dichlorotoluene and dichlorocumene, and these are important as intermediates for synthesis of agricultural chemicals and medicines.
A halogenated benzene derivative is generally obtainable as a mixture of isomers through halogenation of benzene, alkyl benzene or halogenated alkyl benzene and is provided by isolating the desired isomer from such mixture of isomers. Separation of the isomer is generally made by distillation, crystallization or adsorption. But, as these isomers are not much different in boiling or freezing point, a conventional distillation or crystallization method is hardly applicable.
On the other hand, there have recently been developed methods of isomerizing a dialkylbenzene such as xylene in the presence of a catalyst (U.S. Pat. No. 4,409,413) and a method of adsorptive separation of a mixture of alkylbenzene isomers with a zeolite adsorbent (Japanese Examined Patent Publication No. 15681/1977 and Japanese Examined Patent Publication No. 38202/1983). According to these methods, the desired isomer is obtainable at a considerable purity. Further, by feeding the remaining components after separation to an isomerization process and thus isomerizing them, and then separating the desired isomer in adsorptive separation once more, it is possible to ultimately produce the desired isomer only.
However, when said method of isomerization and adsorption separation is applied to production of halogenated benzene derivatives, degradation of the zeolite adsorbent occurs gradually, resulting in reduction of productivity.